1. Field of the Invention
The present invention relates to conductive particles and a production method thereof, and to an anisotropic conductive film, a bonded structure and a bonding method using such conductive particles.
2. Description of the Related Art
To connect circuit members each other, such as a connection between a liquid crystal display device and a tape carrier package (TCP), a connection between a flexible printed circuit (FPC) and TCP, and a connection between a FPC and a printed circuit board, a circuit connecting material (e.g., anisotropic conductive film), in which conductive particles are dispersed in a binder resin, is used. In recent years, when a semiconductor silicon chip is mounted on a substrate, in order to connect circuit members to each, so-called “flip chip mounting” is employed in which the semiconductor silicon chip is directly bonded face down on the substrate without using a wire bond. In this flip chip mounting, circuit connecting materials, such as an anisotropic conductive adhesive, are used for connecting circuit members to each other.
The anisotropic conductive film generally contains a binder resin and conductive particles. As the conductive particles, for example, nickel (Ni) based conductive particles have been popular as hardness thereof is high, and a cost can be reduced compared to use of gold (Au) based conductive particles.
There is disclosed, as the nickel (Ni) based conductive particles, for example, conductive particles each containing a resin particle and a conductive layer which is formed on the resin particle and contains nickel or nickel alloy, where the conductive layer has a surface in which irregularities are formed with aggregates of cluster particles, and the conductive layer has a phosphorus content of 2% to 8% (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2006-302716).
Onto these conductive particles, however, surface modification has not be performed, and therefore the conductive particles have low corrosion resistance (moisture resistance), which leads to low connection reliability.
There is disclosed, as the nickel (Ni) based conductive particles, conductive particles each containing a resin particle, and a conductive layer formed on a surface of the resin particle, where the conductive layer contains an amorphous nickel plating layer having a phosphorus content of 10% to 18%, and a crystalline nickel plating layer having a phosphorus content of 1% to 8% (see, for example, Japanese Patent (JP-B) No. 4235227).
The amorphous structure in the conductive layer has low hardness, and no surface modification has been performed onto these conductive particles, and therefore the conductive particles have low corrosion resistance, which leads to low connection reliability.
There is disclosed, as the nickel (Ni) based conductive particles, conductive particles each containing a resin particle a surface of which is covered with a multilayer conductive film in which a metal plating coating film containing nickel and phosphorus is provided on a surface of the resin particle, and a gold layer provided as an outermost surface of the multilayer conductive film, where the metal plating composition of the metal plating coating film in the region that is from the side of the base particle to 20% or less of the thickness of the metal plating coating film contains phosphorus in an amount of 10% by mass to 20% by mass, and the metal plating composition of the metal plating coating film in the region that is from the top surface of the metal plating coating film to 10% or less of the thickness of the metal plating coating film contains phosphorus in an amount of 1% by mass to 10% by mass (see, for example, JP-A No. 2006-228475).
These conductive particles however have portions having low hardness in their conductive layers, and are not subjected to a surface treatment. Therefore, corrosion resistance thereof is low, which leads to low connection reliability.
There are disclosed, as the nickel (Ni)-based conductive particles, conductive particles each containing a core particle, and a conductive layer formed on a surface of the core particle, where the core particle is a nickel particle, and the conductive layer is a nickel plating layer at surface of which a phosphorus concentration is 10% by mass or lower, and has the average thickness of 1 nm to 10 nm (see, for example, JP-A No. 2010-73681).
However, a surface modification is not performed on these conductive particles, and the corrosion resistance thereof is low, which leads to low connection reliability.
There is disclosed, as the nickel (Ni)-based conductive particles, conductive particles containing an outermost layer having a metal surface constituted of metal atoms including gold and/or palladium, and a nickel layer provided below the outermost layer, where the metal surface is covered with surface modification groups including a sulfur atom at a terminal thereof (see, for example, JP-A No. 2009-280790).
Although a surface treatment is performed on these conductive particles, corrosion resistance of the conductive particles is not improved, and hence having a problem that connection reliability is low.
Accordingly, there are strong demands for conductive particles, which can prevent oxidation of conductive layers, and improve corrosion resistance, without reducing the hardness of the conductive layer.